andesite

n. fine-grained volcanic rock of dark gray color

Andesite (IPA: ) is an igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. The mineral assembly is typically dominated by plagioclase plus pyroxene and/or hornblende. Biotite, quartz, magnetite, sphene are common accessory minerals. Alkali feldspar may be present in minor amounts. The quartz-feldspar abundances in andesite and other volcanic rocks are illustrated in QAPF diagrams. Relative alkali and silica contents are illustrated in TAS diagrams.
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Noun
1. a dark gray volcanic rock
(hypernym) igneous rock

n. andesite

(n.)
An eruptive rock allied to trachyte, consisting essentially of a triclinic feldspar, with pyroxene, hornblende, or hypersthene.